Ray tracing is one of a number of processes by which a computer can generate an image of a notional scene containing, for example, one or more objects illuminated by one or more localised light sources, or by ambient light.
The ray tracing process determines, for each pixel to constitute the image, whether any light rays would pass from the scene through the co-ordinates defining the position of the pixel relative to the scene and to a notional viewing position. The contributions made by any such rays to the notional intensity and colour of light incident on the viewing position are then calculated. This information determines the required brightness and colour for the pixel. A basic ray-tracing method is described in the article entitled "An Improved Illumination Model for Shaded Display", in Communications of the ACM, 26 (6), 342-349 (Whitted 1980).
Ray tracing enables a high resolution of image to be created, and can depict phenomena such as reflection, refraction and light scattering.
However, a large number of calculations have to be performed in order to determine the path (and characteristics) of each light ray, as a result of which a ray tracing method tends to be very slow.